Electrolytic treatment of metals and alloys



ELECTROLYTIC TREATMENT OF METALS AND ALLOYS Percy Allan Charlesworth, Adlington, England No Drawing. Application March 25, 1953 Serial No. 344,670

Claims. (Cl. 204-1405) This invention relates to improvements in the electrolytic treatment of metal surfaces wherein an electrolyte comprising a mixture of sulphuric acid and phosphoric acid or sulphuric acid alone, the electrolyte being of high acid concentration, is employed and the article to be polished is made the anode.

in the specification of my U. S. Patent No. 2,594,124 an electrolytic polishing process is described having an electrolyte based on a mixture of sulphuric acide or phosphoric acid or on sulphuric acid alone to which is added a small amount of the aromatic amino compound, e. g. aniline.

I have now found and this discovery forms the basis of the present invention that stainless steel and other ferrous alloys with chromium and/or nickel; plain carbon steels and similar ferrous alloys; nickel and its alloys; chromium and its alloys and cobalt and its alloys can be satisfactorily electrolytically treated for the purpose of brightening, polishing, electro-machining, shaping, cutting and stress relieving or the like using an electrolyte based on a mixture of sulphuric acid and phosphoric acid or on sulphuric acid alone to which a relatively small amount of a heterocyclic compound or compounds of the type in which the heterocyclic molecule contains at least one ring structure having present in the ring at least two heterocyclic atoms one of which is nitrogen.

Although the invention is not limited thereto, I have founnd that it is particularly advantageous when the electrolyte has an acid concentration of at least 50% by weight of the electrolyte or more generally speaking has a combined sulphate and phosphate content which When expressed as sulphuric acid and phosphoric acid respectively represents at least 50% of the electrolyte and the ratio of sulphuric acid and phosphoric acid initially in the electrolyte exceeds 5:3.

The proportion of the additive necessary is small and falls within the range of 0.3% to by weight of the electrolyte according to the particular additive or additives employed and the work the electrolyte is required to do.

Polishing processes using an electrolyte according to the present invention can be carried out using current densities within the range of 0.3 to 5 amps. per square inch. Higher current densities may be used for treatment requiring greater metal removal, e. g. electro-machining.

Generally a heterocyclic compound of the type referred to, to be satisfactory as an additive should saitsfy the following requirements:

(1) It should be effective at low concentrations, i. e. between 0.3% and 10% by weight of the electrolyte.

(2) It should have a reasonable life.

(3) Deleterious reaction products should be capable of removal from the electrolyte.

(4) It should not cause excessive frothing or foaming nor give ofi malodorous or toxic vapors during the polishing process.

The following compounds are illustrative of the type of 2,820,? Patented Jan. 21, 1952 molecular configuration of the additives: morpholine phenyl morpholine and thialdine, the structural formula of the latter compound being:

CH-NH S\ CHCHI CH-S Parts by weigh H2804 5. H PO 2i 2 to 3' Morpholine 2 t0 1 Example 1.-Stainless steel.--A current density of 1 amp. per square inch and a temperature of 50-60 C.

Example 2.Plain clarbon steels and low alloy steels A current density of 1 amp. per square inch and 2 temperature of 85 C.

Example 3.Stainless iron, 2. g. ferrous alloys having 17% chromium content.A current density of 1 amp per square inch and a temperature of 85 C.

Example 4.An alloy in which the proportions of the main constituents are Ni55%, Cr20%, C0-20% e. g. Nimonic 90.--A current density of 1.8 amps per square inch and a temperature of 30 C.

Example 5.An alloy in which the proportions of the main constituents are Ni75%, Cr20%, e. g. Nimoniz 8 0.-A current density of 2.0 amps. per square inch anc a temperature of 30 C.

Example 6.An alloy in which the proportion of the main constituents are Ni%, Cr20%.A curren density of 1.0 amp. per square inch and a temperature 0: 30 C.

The additives and processing conditions employed are related to the metal or alloy being treated and the resul desired. The time of treatment depends on the amoun of metal to be removed; thus for polishing the time taker in the foregoing examples would be about 10 minute: whilst for machining it might be 30 minutes or longer Further the current density employed can also be varied ac cording to the amount of metal to be removed.

The water and metal content of the electrolyte depend: on its particular application and various forms of agitatioi may be employed as required.

I claim:

1. A method of anodically removing metal from th surface of a metallic body belonging to the group con sisting of iron, nickel, chromium, cobalt and alloys 0 each, characterized by immersing at least a surface por tion of said metallic body in an electrolyte solution con taining at least 50% by weight of said solution of acir constiutents belonging to the group consisting of sulphurii acid and of a mixture of sulphuric and phosphoric acid, tht ratio of sulphuric acid in said mixture to phosphoric acit being greater than 5 to 3, said electrolyte solution alsr containing between 0.3% and 10% by weight of sair solution of an additive belonging to the group consisting o: morpholine and morpholine derivatives; and passing current through said metallic body and said electrolyte solution.

2. A method of anodically removing metal from the surface of a metallic body belonging to the group consistng of iron, nickel, chromium-cobalt and alloys of each, lharacterized by immersing at least a surface portion of aid metallic body in an electrolyte solution containing at least 50% by weight of said solution of acid constituents velonging to-the group consisting of sulphuric acid and f a mixture of sulphuric andpho'sphori'c acid, the ratio |f sulphuric acid in said mixture 'to phosphoric acid being ;reater than to 3, said;e lectrolyte solution also containng between 0.3% and by weight of said solution of morpholine; and passing cuflr'i'tthrough said metallic |ody and said electrolyte solutions 3. A methodof anodically removing metal from the 1 taining at least 50% by weight of said solution of sulurfa'ce of a metallic body belonging to the group. consistugpfiiron, nickel, chromium,'cobal t andyalloys of each, haracterized .by immersing at; leastua surface portion of aid metallic bodyinan electrolyte-solution containing at east 50% by weight of said solution of acid constituents belonging to the group consisting of sulphuric acid and of a mixture of sulphuric and phosphoric acid, the ratio of sulphuric acid in said mixture to phosphoric acid being greater than 5 to 3, said electrolyte solution also containing between 0.3% and 10% by weight of said solution of thialdine; and passing current through said metallic body andsaid electrolyte solution. 7

5. A method of anodically removing metal from the surface of a metallic body belonging to the group consisting of iron, nickel, chromium, cobalt and alloys of each, characterized by immersing at least a surface portion of said metallic body in an electrolyte solution conphuric acid, said electrolyte solution also-containing between 0.3% and 10% by weight of said solution of an additive belonging to the group consisting of morpholine and morpholine derivatives; and passing current through elonging to the group consisting of sulphur acid and of A mixture of sulphuric and phosphoric acid, the ratio of ulphuric'i acid-1 in said mixture to phosphoric acid being reater than Ste 3, said electrolyte solution also containng between 0.3% and 10% by weight of said solution of said metallic body and said electrolyte solution.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A METHOD OF ANODICALLY REMOVING METAL FROM THE SURFACE OF A METALLIC BODY BELONGING TO THE GROUP CONSISTING OF IRON, NICKEL, CHROMIUM, COBALT AND ALLOYS OF EACH, CHARACTERIZED BY IMMERSIN AT LEAST A SURFACE PORTION OF SAID METALLIC BODY IN AN ELECTROLYTE SOLUTION CONTAINING AT LEAST 50* BY WEIGHT OF SAID SOLUTION OF ACID CONSTITUENTS BELONGING TO THE GROUP CONSISTING OF SULPHURIC ACID AND OF A MIXTURE OF SULPHURIC PHOSPHORIC ACID, THE RATIO OF SULPHURIC ACID IN SAID MIXTURE TO PHOSPHORIC ACID BEING GREATER THAN 5 TO 3, SAID ELECTROLYTE SOLUTION ALSO CONTAINING BETWEEN 0.3% AND 10% BY WEIGHT OF SAID SOLUTION OF AN ADDITIVE BELONGING TO THE GROUP CONSISTING OF MORPHOLINE AND MORPHOLINE DERIVATIVES, AND PASSING CURRENT THROUGH SAID METALLIC BODY AND SAID ELECTROLYTE SOLUTION. 